Hertz's partnership with Amazon is another step in the e-commerce giant's slow march into auto sales. The deal could be a boon for the rental car giant, which is trying to sell more of its cars directly to consumers. Some experts say the shift toward direct online sales, especially involving e-commerce giants like Amazon, could spell trouble for dealerships, possibly even large publicly traded companies such as AutoNation, Group1, Sonic Automotive, Penske, and Asbury. Wholesale auction companies such as Manheim and AVC are also liable to be watching the shift, as direct to consumer sales could threaten their inventories. Why...